The White House's lead economist Jason Furman dismissed speculations of the so-called "death spiral," saying subsidies will prevent the descent.

"I think it is absolutely impossible for these markets to enter a death spiral," Mr. Furman, the chair of the White House's Council of Economic Advisers, told Vox. "It is frankly crazy that people are leaping to the death spiral conversation," he said.

While 15 percent to 17 percent of marketplace enrollees do not receive subsidies and may exit the market because of rising premiums and limited plan choice, Mr. Furman said there is no incentive for individuals eligible for subsidies to leave the market. In turn, he said many enrollees will stay and sustain a healthy risk pool.

"When you have 84 percent in the marketplace subsidized — or two-thirds if you include the whole individual market — that effectively arrests the death spiral, that effectively prevents it," Mr. Furman said, according to the report.